In an effort to keep pace with increasingly demanding bonding conditions and to comply with the numerous circumscribing environmental regulations, much of the research in the adhesive field is currently being directed towards developing a robust adhesive that can be applied as an aqueous formulation so as to avoid the use of volatile solvents. The fruits of these research efforts can be seen in recently issued U.S. Pat. Nos. 4,988,753 and 5,036,122. U.S. Pat. No. 4,988,753 describes an aqueous dispersion for bonding natural and synthetic elastomers to metallic and non-metallic substrates under vulcanizing conditions. The adhesive composition contains a mixture of chlorosulfonated polyethylene and vinyl chloride/vinylidene chloride/acrylic acid copolymer, an organic polynitroso compound, and a coreactive compound selected from diallyl acrylamide and phenylene bis-maleic acid imide. The adhesive composition may optionally contain other additives such as metal oxides, lead salts, and peroxides.
U.S. Pat. No. 5,036,122 describes an aqueous adhesive composition containing a latex of a polymerized conjugated diene, a poly-C-nitroso compound, and a polymaleimide compound which is a polymer of a bis-maleimide. The polymerized conjugated diene is preferably poly-2,3-dichlorobutadiene or poly-1,1,2-trichlorobutadiene. The adhesive may optionally contain additives such as carbon black, metallic oxides, and surfactants.
U.S. Pat. No. 4,119,587 describes an adhesive composition containing a halogen-containing polyolefin, an aromatic nitroso compound, and a lead salt. The composition may optionally contain a maleimide compound. The use of a volatile organic solvent is also disclosed.
Many previously developed adhesive compositions such as the composition disclosed in U.S. Pat. No. 4,119,587 described above require the use of an organic solvent and/or the use of a lead salt, both of which can be detrimental to the environment. Also, many previously developed aqueous adhesive compositions such as those disclosed above require the use of an additional adhesive component, such as a primer component, in order to attain acceptable adhesive performance levels. A primer component is particularly needed in rubber-to-metal applications involving exposure to adverse environmental conditions where the metal surface is susceptible to corrosion that can degrade the adhesive bond. Furthermore, many aqueous adhesive compositions can only be utilized to bond a narrow range or class of substrates.
Traditional adhesives utilized for bonding elastomeric materials to metal are also frequently susceptible to the high temperature conditions experienced in the molding devices utilized in the bonding process. The molding devices which position and support the adhesive-coated metal parts are typically preheated or prebaked before the molten elastomeric material is applied to the metal part. This prebake frequently interferes with the bonding ability of the adhesive composition applied to the metal surface.
A one-component aqueous adhesive composition is needed which utilizes environmentally safe components to provide a robust adhesive bond to numerous types of substrates.